In recent years, since electrochemical devices, for example, an electrical double layer capacitor, a lithium-ion secondary battery, and the like, have the advantages of being able to easily realize reduction in size and weight thereof, they are expected to be used for power supplies for mobile devices, back-up power supplies, auxiliary power supplies for electrical or hybrid vehicles and the like. There have therefore been many attempts to improve their performance.
An electrode used in the electrochemical devices usually contains the following constituents: a current collector foil made of aluminium, stainless-steel, or the like; and an electrode layer consisting of a mixture of an active material with high-specific surface area, such as, activated carbon, a conductive additive, such as, a conductive carbon and a binder. For reducing internal resistance and increasing capacitance of the device, the activated carbon used as one of the active materials is typically processed by modifying a surface part thereof, increasing its specific surface area and the like with conventional activation methods, such as an alkaline activation method. A modification with such an activation method is also utilized for increasing capacitance of a polarizable electrode for an electrical double layer capacitor.
Japanese Unexamined Patent Publication (Kokai) No. 11-317333 discloses a carbon material for an electrical double layer capacitor which has a microcrystal carbon similar to a graphite-like carbon manufactured by operating an activation processing to a carbon material, wherein the interlayer distance of the microcrystal carbon is 0.365 nm to 0.385 nm. Japanese Unexamined Patent Publication (Kokai) No. 2002-25867 discloses a nonporous carbon material for use in an electric double-layer capacitor, wherein the material consists of microcrystalline carbon like graphite, the carbon being a nonporous carbon having a specific surface area of less than 270 m2/g, and wherein interlayer distance of the carbon is 0.360 to 0.380 nm.